a level physics notes on unit 7 - SUR (AKA materials)

We can replace many tissues with prosthetics
eg . Skin
bone
lens in eyes
valve in hearts
cartilidge
some muscles eg heart
.




nerves (wiring)



When replacing mechanical tissues (movement /support) it is important ,
to
match the PROPERTIES of the original tissue with the replacement's.


Stiffness is of limited use as it is specific to a sample ,
so

that
generic property material
eg DENSITY
we need a
of a .




tells us how a material behaves when a force is applied

2
↓
--
YOUNGS MODULUS
Wh

↑--
Y
F
>
-

&
Al
- I

compressed




STRESS =
Oce Nim(pal [PREssum]
G

STRAIN tension th
E

YOUNG'S STRESS Strain
(Pa) is unitless
=
as
MODULUS RAIN
-
E - o



S
STRESS (Pa)
E o
vo = YOUNGS
T MODULUS E




STRAIN E

, BONE
E = 2x10"Pa-HUGEi need big forces to deform bones by
small amounts




CARTILAGE STEEL COPPER
E = 5x10
°
Pa E = 2x10"Pa E = 1 -
2x10"Pa



Im
T
↑
Y
↑
am
3m 3m
== 2x10n

IIm
-



&
10 cm




(0" 33x10"Pa
E-
= f = = 0 .




6


3
= =
E =


3340" = 0 .

33x10



o 565
=
3


m
= .




3
3 =
0012 = 4 8x10-
.




01 = 1 2c m
.




2 5
.




z =
22565x102 =
7 .
43x10'4Pa
3
4 8x10
-



.